1. Field of the Invention
The present invention relates to a shading compensation device, a shading compensation value calculation device and an imaging device, and relates to, for example, an excellent shading compensation device, shading compensation value calculation device and imaging device which are employed at a time of compensating for shading of an image signal which is outputted from a high-pixel count image capture device.
2. Description of the Related Art
In an image generated by a CCD image sensor, because of effects such as variations in transparency of a lens and the like, a so-called shading effect occurs, in which a central portion of the image is brighter than a peripheral portion. Accordingly, various techniques relating to shading compensation, in order to prevent the effects of such shading, have been disclosed.
For example, CCD camera shading compensation circuits have been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 5-83622) which are formed such that shading does not vary when the aperture of a lens is altered. The shading compensation circuit recited in JP-A No. 5-83622, in response to the size of a lens aperture, designates an address of shading compensation data which has been written to a ROM beforehand, and alters shading compensation signals in accordance with shading compensation data read from the ROM.
Further, distance detection devices for vehicles have been disclosed (see, for example, JP-A No. 6-273171) which prevent effects of shading of an imaging system and improve accuracy of detection of distances. The distance detection device for a vehicle recited in JP-A No. 6-273171 in advance has stored shading compensation data in a memory and, by multiplying the shading compensation data stored in the memory with data of respective pixels of a digital image, provides a shading-compensated digital image.
Further yet, image processing devices have been disclosed (see, for example, JP-A No. 6-319042) which are capable of shading compensation which is not influenced by noise, surface texture of a proofing plate or the like. The image processing device recited in JP-A No. 6-319042 calculates average values of brightness data for each of a plurality of regions, infers brightnesses of the pixels in the regions, calculates shading compensation values on the basis of the inferred pixel brightnesses, and utilizes these shading compensation values to correct the brightness data.
Because of increases in pixel numbers of solid-state image capture devices and reductions in cell sizes, there is a trend for shading amounts of respective colors to differ in accordance with exit pupil, aperture and the like. Hence, when shading amounts for respective colors are different, a problem arises in that colors differ between locations of a screen, and white balance is also affected. However, consideration has not been extended to differences in shading amounts for respective colors in any of the technologies recited in JP-A No. 5-83622, JP-A No. 6-273171 and JP-A No. 6-319042, and it has not been possible to solve the problems described above.